You’ll be glad to know that the workaround seems to have worked.
Sorry, it is the same on this website’s preview calendar page, so it’s surely not Siteground.
Longer appointments show as one-hour appointments in full view – week.
However, I’ve updated both plugins to no avail, plus in full view – week – it’s still showing each event as being one-hour in duration.
Same on the calendar preview page.
I’m the bearer of bad news today.